Bipolar coordinate solution of pillar stability for salt cavern energy storage

Abstract

As one of the crucial carriers for large-scale deep underground energy storage, salt caverns have great prospects for development. Pillar in salt cavern energy storage (SCES) refers to the preserved rock mass between adjacent salt caverns, which plays a crucial role in maintaining the stability of the SCES. Given the limited research on the analytical solutions for assessing the pillar stability of SCES, this study proposes a stability analysis method that includes horizontal and vertical profiles. In the analysis of the horizontal profile, elasticity theory and the Mohr-Coulomb strength criterion are comprehensively utilized to determine the critical operating pressure of the cavern, the range of plastic zones, and the stress distribution within the pillar. In the analysis of the vertical profile, the shear stresses and additional axial stress caused by uncoordinated deformation at the interfaces are analyzed. Through case analyses involving different operating modes and pillar widths and by comparing the results with the results of numerical simulations, the following conclusions are drawn: 1) Damage is most likely to occur on one side of the pillar adjacent to the cavern, which is crucial for cavern stability; 2) Maintaining an alternating pattern of high and low pressure (asynchronous injection-production) in two adjacent caverns rather than maintaining equal pressure in two caverns (synchronous injection-production) can reduce the critical operating pressure of the SCES to some extent, thereby improving energy storage efficiency; and 3) When the width of the pillar is low, the radial stress may decrease at the center of the pillar, potentially leading to plastic failure. 4) Uncoordinated deformation causes an increase in the range of the plastic zone around the cavern and increases the likelihood of damage within the interlayer. These findings provide important theoretical methods and guidance for the stability assessment of pillars in SCES.